Chemical disinfestation and metabolic integrity of soil

Summary Field disinfestation in autumn with normal or increased dosages of 1,3-dichloropropene, metham-sodium or chloroform, and in spring with ethoprophos, did not, or hardly, affect the degradationin situ of some herbicides applied in spring. However, during laboratory incubation of samples from the disinfested plots, sometimes decreased herbicide degradation rates or increased lag phases were found.The top few centimetres of the field soil, on which the herbicides were sprayed, apparently largely escaped fumigation. Accordingly, effects of fumigation on herbicide degradation, organic matter and N metabolism were stronger in samples from the 10–20 cm layer than in samples from 0–10 cm.In the laboratory fumigation of soil samples with CHCl₃ was much more drastic in inhibiting herbicide degradation, N mineralisation and nitrification; inoculation with 10% fresh soil, however, greatly accelerated the recovery of these processes. Therefore, in practice prolonged or drastic effects of chemical soil disinfestation on metabolic integrity of the soil are not to be expected.     

Suppression of tomato bacterial wilt by anaerobic soil disinfestation and associations with production of antagonistic compounds

Plant and Soil - Anaerobic soil disinfestation (ASD) has been proven to be an effective and environmentally friendly method for controlling soil-borne plant diseases. Mechanisms of ASD-mediated...     

Degradation of the fungal cell wall by clostridial strains isolated from soil subjected to biological soil disinfestation and biocontrol of Fusarium wilt disease of spinach

Applied Microbiology and Biotechnology - Biological soil disinfestation (BSD) involves elimination of soil-borne plant pathogens in an environmentally friendly manner. Two anaerobic bacterial...     

Ethyl formate fumigation for the disinfestation of red imported fire ants Solenopsis invicta Buren

The red imported fire ant, Solenopsis invicta Buren, is a serious invasive pest of quarantine significance. Potential establishment of this ant is of great concern in S. invicta free countries such as South Korea, where there have been multiple recent interceptions. The majority of those detections have been concentrated around main port areas of imported common trade containers, suggesting that disinfestation of the containers, in addition to inspection and disinfestation of containers with agricultural commodities, is necessary for the prevention of S. invicta introduction. So far, however, no regulations and protocols are in place for inspection, detection, and disinfestation of S. invicta in such containers. As a first step toward supporting such regulation, we investigated whether S. invicta could be effectively controlled using ethyl formate, a methyl bromide alternative. Ethyl formate fumigation treatment was effective in controlling 99.9% of S. invicta workers and female alates at 46.1 and 37.7 g h m⁻³ at 13 °C and 23 °C respectively. Our results provide evidence to support its use to disinfest S. invicta in containers. We discuss additional factors that need to be considered to develop disinfestation protocols for S. invicta in commerce shipping containers.     

Mycorrhizal inoculation of cloned hazels by Tuber melanosporum: effect of soil disinfestation and co-culture with Festuca ovina

A pot experiment was conducted to determine the effects of soil disinfestation and presence of Festuca ovina L. on the formation of Tuber melanosporum Vitt. mycorrhizae by Corylus avellana L. Festuca ovina reduced colonization of young hazels by T. melanosporum. Co-culture with F. ovina resulted in necrosis of hazel roots, leading to 33% plant mortality. The surviving hazels were poorly colonized by T. melanosporum and highly colonized by other symbionts. Roots of F. ovina did not seem to attract mycelium or to be infected by T. melanosporum. Relatively poor mycorrhizal colonization developed in non-disinfested soil containing native inoculum of Tuber melanosporum. Mycorrhization by T. melanosporum developed very efficiently in disinfested soil inoculated with a spore suspension with relatively little colonization by competing symbionts. Growth of host plant was also affected.     

低温茬口空闲期土壤强还原消毒对西瓜枯萎病的影响

为探明低温茬口空闲期土壤强还原消毒(RSD)对西瓜枯萎病的防控效果,设置对照(CK)、淹水对照(FCK)、淹水添加2%(w/w)苜蓿粉(AL)、0.25%(w/w)乙酸(AC)以及AL+AC的RSD处理进行西瓜盆栽试验,采用定量PCR和Illumina Miseq等测定真菌、尖孢镰刀菌数量及真菌群落组成,并统计发病率和产量。结果表明: 与CK相比,FCK和各RSD处理均能显著降低尖孢镰刀菌数量及其在真菌中的比例,杀菌效果达86.1%～94.6%;AL、AC以及AL+AC处理显著增加了西瓜产量,降低了枯萎病发病率,且枯萎病防控效果分别为63.2%、73.7%和94.7%,而FCK与CK无显著差异。与CK相比,AL和AC处理显著改变了土壤真菌群落组成,FCK处理对真菌群落无显著影响;RSD处理均显著增加了柄孢壳属、假散囊菌、地丝菌、粪盘菌、韦斯特壳属以及久浩酵母菌等优势属的相对丰度,且其中大部分与尖孢镰刀菌数量及其在真菌中的比例以及发病率呈显著负相关关系。综上,低温茬口空闲期的RSD处理可以通过重塑真菌群落组成有效防控西瓜枯萎病的发生。     

The establishment of axenic seed and embryo cultures of endangered Hawaiian plant species: special review of disinfestation protocols

More than one third of the USA’s federally listed endangered and threatened plants are endemic to Hawaii. Because of the accelerating rate of environmental pressures resulting from habitat degradation to loss, the Hawaiian Rare Plant Program (HRPP, Lyon Arboretum, Honolulu, Hawaii) utilizes in vitro culture and seed storage to rescue, recover, and restore Hawaii’s most critically endangered native plant taxa. These in vitro methods complement existing ex situ and in situ efforts in the state. Wild-collected seeds tend to be hard to clean, and obtaining contamination-free seeds or embryos without damage or over sterilization is one of the most difficult obstacles in the successful establishment of in vitro cultures. Loss of rare and valuable propagation material occurs when seed samples succumb to contamination or mortality during the initial disinfestation stage. This study reviews pre-treatments and provides examples of three general disinfestation protocols successfully used in the HRPP to establish axenic ovule and embryo cultures of some endangered Hawaiian species. Three disinfestation protocols are described: bleach sterilization, gas sterilization, and ethanol dip and flame. Since 1998, the HRPP has been successful in establishing in vitro cultures of 135 endangered Hawaiian plant taxa representing 30 genera.     

Irradiation disinfestation of apple maggot (Diptera: Tephritidae) in hypoxic and low-temperature storage

Apple maggot, Rhagoletis pomonella (Walsh), is a quarantine pest of apples, Malus domestica Borkhausen, and pears, Pyrus communis L., shipped from much of the United States and Canada. As such, these fruits shipped from infested areas to uninfested areas must undergo a quarantine disinfestation treatment. The objective of this research was to develop irradiation quarantine treatments against apple maggot considering that fruit hosts may be stored under hypoxic or cold conditions when they are irradiated. Hypoxia increased from 30.5 to 35.7 Gy (17%) the estimated dose to achieve 99% prevention of the full pupal stage from irradiated third instars in apples compared with ambient atmospheres. However, 50 Gy completely prevented the full pupa in 22,360 and 15,530 third instars, respectively, irradiated in apples in ambient and hypoxic atmospheres. There was no difference in development to the full pupal stage in apple maggot third instars held at 1 or 24 degrees C when irradiated with 20 Gy. Because the maximum dose measured when 50 Gy was sought was 57 Gy, the latter should be the dose recommended for quarantine disinfestation of host fruits of the apple maggot. Apples and pears tolerate much higher doses.     

Exploring warm-season cover crops as carbon sources for anaerobic soil disinfestation (ASD)

Background and aims

Anaerobic soil disinfestation (ASD) has been shown to be an effective strategy for controlling soilborne plant pathogens and plant-parasitic nematodes in vegetable and other specialty crop production systems. Anaerobic soil disinfestation is based upon supplying labile carbon (C) to stimulate microbially-driven anaerobic soil conditions in moist soils covered with polyethylene mulch. To test the effectiveness of warm-season cover crops as C sources for ASD, a greenhouse study was conducted using a sandy field soil in which several warm-season legumes and grasses were grown and incorporated and compared to molasses-amended and no C source controls.

Methods

Greenhouse pots were irrigated to fill soil porosity and covered with a transparent polyethylene mulch to initiate a 3-week ASD treatment prior to planting tomatoes. Soilborne plant pathogen inoculum packets, yellow nutsedge (Cyperus esculentus L.) tubers, and Southern root-knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood; M.i.) eggs and juveniles were introduced at cover crop incorporation.

Results

In nearly all cases, ASD treatment utilizing cover crops as a C source resulted in soil anaerobicity values that were equal to the molasses-amended fallow control and greater than the no C source fallow control. In trial 1, Fusarium oxysporum Schlechtend.:Fr. (F.o.) survival was reduced by more than 97% in all C source treatments compared to the no C source control but there was no effect of C source in Trial 2. Carbon source treatments were inconsistent in their effects on survival of Sclerotium rolfsii Sacc. (S.r). In general, the number of M.i. extracted from tomato root tissue and root gall ratings were low in all treatments with cover crop C source, molasses C source, or composted poultry litter. Germination of yellow nutsedge tubers was highest in the no C source control (76%), lowest in the molasses control (31%), and intermediate from cover crop treatments (49% to 61%).

Conclusions

Warm-season cover crops have potential to serve as a C source for ASD in vegetable and other crop production systems, but more work is needed to improve consistency and further elucidate mechanisms of control of soilborne plant pathogens and weeds during ASD treatment utilizing cover crops.     

The microbial changes during the biological control of cucumber damping-off disease using biocontrol agents and reductive soil disinfestation

Cucumber damping-off disease mainly caused by Rhizoctonia solani leads to serious loss in agricultural production. In this study, the effective and environmentally friendly methods, using two biological agents combined with applying organic matter or reductive soil disinfestation (RSD), were performed to control the disease. Real-time PCR and MiSeq pyrosequencing were used to investigate the microbial community changes during the biocontrol process. The results showed that the applications of organic matter and antagonists (Ant) significantly decreased R. solani population and disease incidence, and increased soil microbial population and activity. However, antagonists application combined with RSD (RSD + Ant) behaved much better in nearly all aspects, and facilitated to maintain the population and activity of antagonists. Compared to the applications of organic matter and antagonists, the combination of RSD and antagonists changed soil microbial community structure to a larger extent. In conclusion, the applications of biocontrol agents and organic matter improved soil microbial community and decreased cucumber damping-off disease incidence, but the combination of RSD and the antagonists was a more promising method for the improvement of soil microbial community and the stable and successful control of the disease.     

Proliferation of diversified clostridial species during biological soil disinfestation incorporated with plant biomass under various conditions

Biological soil disinfestation (BSD) involves the anaerobic decomposition of plant biomass by microbial communities leading to control of plant pathogens. We analyzed bacterial communities in soil of a model experiment of BSD, as affected by biomass incorporation under various conditions, to find out the major anaerobic bacterial groups which emerged after BSD treatments. The soil was treated with Brassica juncea plants, wheat bran, or Avena strigosa plants, irrigated at 20 or 30 % moisture content and incubated at 25–30 °C for 17 days. The population of Fusarium oxysporum f. sp. spinaciae incorporated at the start of the experiment declined markedly for some BSD conditions and rather high concentrations of acetate and butyrate were detected from these BSD-treated soils. The polymerase chain reaction-denaturing gradient gel electrophoresis analysis based on the V3 region of 16S rRNA gene sequences from the soil DNA revealed that bacterial profiles greatly changed according to the treatment conditions. Based on the clone library analysis, phylogenetically diverse clostridial species appeared exceedingly dominant in the bacterial community of BSD soil incorporated with Brassica plants or wheat bran, in which the pathogen was suppressed completely. Species in the class Clostridia such as Clostridium saccharobutylicum, Clostridium acetobutylicum, Clostridium xylanovorans, Oxobacter pfennigii, Clostridium pasteurianum, Clostridium sufflavum, Clostridium cylindrosporum, etc. were commonly recognized as closely related species of the dominant clone groups from these soil samples.     

Response of Ceratitis capitata, Bactrocera dorsalis, and Bactrocera cucurbitae (Diptera: Tephritidae) to metabolic stress disinfection and disinfestation treatment

Metabolic stress disinfection and disinfestation (MSDD) is a postharvest treatment designed to control pathogens and arthropod pests on commodities that combines short cycles of low pressure/vacuum and high CO2 with ethanol vapor. Experiments were conducted to evaluate the effect of MSDD treatment on various life stages of Ceratitis capitata (Wiedemann), Mediterranean fruit fly; Bactrocera dorsalis Hendel, oriental fruit fly; and Bactrocera cucurbitae Coquillett, melon fly, in petri dishes and in papaya, Carica papaya L., fruit. In some experiments, the ethanol vapor phase was withheld to separate the effects of the physical (low pressure/ambient pressure cycles) and chemical (ethanol vapor plus low pressure) phases of treatment. In the experiments with tephritid fruit fly larvae and adults in petri dishes, mortality was generally high when insects were exposed to ethanol and low when ethanol was withheld during MSDD treatment, suggesting that ethanol vapor is highly lethal but that fruit flies are quite tolerant of short periods of low pressure treatment alone. When papaya fruit infested with fruit fly eggs or larvae were treated by MSDD, they produced fewer pupae than untreated control fruit, but a substantial number of individuals developed nonetheless. This suggests that internally feeding insects in fruit may be partially protected from the toxic effects of the ethanol because the vapor does not easily penetrate the fruit pericarp and pulp. MSDD treatment using the atmospheric conditions tested has limited potential as a disinfestation treatment for internal-feeding quarantine pests such as fruit flies infesting perishable commodities.     

Optimizing metabolic stress disinfection and disinfestation components to control Pseudococcus longispinus

Metabolic stress disinfection and disinfestation (MSDD) has been demonstrated to effectively control longtailed mealybug, Pseudococcus longispinus (Targioni Tozzetti). Standard components previously used for testing MSDD system included a 30-min physical phase of short cycles pressure changes followed by a 60-min chemical phase using ethanol vapor at 10 kPa. This study investigated the effect of varying the following MSDD components on mealybug mortality: duration of the physical and chemical phases, ethanol concentration, and extent of vacuum during the chemical phase. Mealybug mortality responses were analyzed, and the components were optimized using binary logistical regression to achieve 99% mortality of three life stages of the longtailed mealybug (adults, second- and third-instar nymphs and crawlers). Data indicated that the optimal components to achieve 99% mortality of all life stages were a 30-min physical phase and a 45-min chemical phase with 275 mg/liter ethanol at 30 kPa. Optimized components were obtained using binary logistical regression models. These optimized components yielded a 15-min reduction in total treatment time and a 20-kPa decrease in pressure during the chemical phase. Achievement of optimal insecticidal efficacy required all four MSDD components. Nevertheless, optimization and validation achieved 17 and 22% reductions in duration of treatment time and extent of vacuum, respectively.     

New feasible quarantine disinfestation using ethyl formate for termites and ants on imported lumber

The interception of exotic ants and termites from stone and lumber imported into Korea is on the rise, including Solenopsis invicta. Currently, a relatively long exposure (24 h) of methyl bromide (MB) fumigation is the only practical disinfestation option for exotic ants and termites on imported stone and lumber. In this study, ethyl formate (EF) wase evaluated as a potential MB alternative to disinfest ants and termites in imported lumber, with a focus on S. invicta. As S. invicta is not established in Korea, we first determined whether Reticulitermes speratus, established in Korea, could be considered as an EF surrogate of S. invicta. From 1 h EF fumigation trials, workers of S. invicta were more sensitive to EF than those of R. speratus based on lethal concentration × time causing 99% mortality (LCt_99%), supporting that R. speratus can be used as an EF surrogate of S. invicta. When R. speratus workers were further fumigated with EF for 4 h at four different temperatures, LCt_99% values for R. speratus workers were 108.00, 63.31, 77.24, and 67.24 g h/m³ at 2, 5, 13, and 23 °C, respectively. From scale-up (0.65 m³) and commercial scale (76.4 m³) trials containing two infestation-prone lumber species, lauan (Shorea spp.) and acacia (Acacia spp.), 140 g/m³ EF at >5 °C for 4 h resulted in the complete control of R. speratus workers, suggesting that 140 g/m³ 4 h-EF-fumigation may be applicable as a potential MB-alternative treatment for disinfestation of invasive S. invicta on imported lumber.     

Cold susceptibility and disinfestation of Bactrocera invadens (Diptera: Tephritidae) in oranges

To develop a cold disinfestation treatment for the fruit fly Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) that is rapidly spreading across Africa, research was conducted in Nairobi, Kenya, using flies from a laboratory culture and 'Valencia' orange (Citrus sinensis L. Osbeck) as the host. The developmental rate of B. invadens in Valencia oranges was determined at 28 degrees C, and the third instar was found to be the least susceptible of the egg and larval life stages to cold treatment at 1.1 degrees C in oranges. When 22,449 B. invadens third instars were exposed in oranges to a cold treatment with an approximate midpoint of 1.1 +/- 0.5 degrees C, the results suggested that a period of 16 d would be worthwhile verifying on a larger scale in oranges. Results from the first replicate of 16,617 larvae showed no survivors, but the second replicate of 23,536 larvae had three survivors. Because a longer cold treatment based on a mean temperature of 1.1 degrees C would create logistical difficulties for some export markets, further replicates were conducted at an approximate midpoint of 0.5 degrees C and at mean hourly maximum of 0.9 +/- 0.5 degrees C, for 16 d. After three replicates, in which 65,752 B. invadens third instars in total were treated with no survivors, the Japanese requirement of 99.99% mortality at the 95% confidence level was surpassed. The following treatment protocol for B. invadens larvae in oranges can therefore be recommended: fruit pulp to be maintained at temperatures of 0.9 degrees C or lower for 16 consecutive days.     

Sensitivity of wild and genetic sexing strain Ceratitis capitata to high-temperature disinfestation of Valencia oranges

Abstract:  The purpose of this research was to investigate post-harvest heat treatment of Valencia oranges as an effective disinfestation protocol (fast, no fruit damage) for the Mediterranean fruit fly Ceratitis capitata (Wiedemann). Forced high-temperature air was applied under the following conditions: (a) exposure to air temperature of 56°C, for fast increase of temperature in the interior of the fruit, (b) reduction in air temperature to 47°C when the fruit centre reached 47°C and (c) maintenance of fruits in the chamber for another 30 min. Relative humidity in the treatment chamber was kept between 50% and 65% during treatment. Forced air at 47°C applied for 30 min on eggs before hatch or late third instar larvae (the most heat-tolerant stages) resulted in complete kill. Egg and larval sensitivity to high temperature differed between a wild strain and a laboratory genetic-sexing strain based on white pupa mutation. In this strain males emerge from brown pupae and females from white pupae. In particular, mature eggs from the wild strain were significantly more temperature resistant than eggs from the laboratory strain. Exposure of Valencia oranges of a diameter of 7–7.5 cm to 56°C forced air for about 86 and 99 min was required to increase temperature to 47°C at 1.5 cm depth and the fruit centre respectively. Treated oranges showed no substantial peel or interior deterioration, or change in colour and taste when kept at 25°C and 50–60% RH for a period of up to 1 month following treatment. Treatment in 1% O₂ atmosphere, produced by flushing of CO₂ into the treatment chamber, resulted in about 1°C reduction in killing temperature and faster increase in temperature inside the fruit to a lethal level.     

Postharvest disinfestation of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae) on persimmons: hot water immersion and coolstorage

The mortality response of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae Koch) on persimmons to hot water immersion treatments between 44 and 54 °C was examined, for potential as a quarantine treatment. The mean immersion time for mean 99% mortality (LT₉₉) of diapausing mites at 44 °C was 211 min, and this time decreased with increasing temperature to 3.6 min at 54 °C. Non-diapausing mites were found to be less tolerant to temperatures below 48 °C, with an estimated LT₉₉ of 102 min at 44 °C, but had similar thermotolerance above 48 °C. In 47 °C water the immersion time required to kill 99% of diapausing mites was estimated at 67 min. This time was not reduced by subsequent coolstorage at 0 °C for up to eight weeks. Rather, coolstorage had the effect of keeping mites alive, relative to LT₉₉ estimates calculated for mites stored at 20 °C. Similarly the thermotolerance of mites did not change with increased time in diapause, even though mites in diapause for 12 weeks had high control mortality. Hot water immersion appears to be a potentially useful disinfestation method for persimmons.     

Recent studies of measures to improve basamid soil disinfestation

Basamid micro-granule is used worldwide as a broad spectrum soil fumigant generator and has replaced methyl bromide for many applications. A lot is known for decades regarding the factors determining the success of the application from soil preparation and conditions to the application and soil sealing or soil tarping, as well as the operations and hygienic measures after the fumigant contact time. This paper explains last 6 years studies regarding the improvement of application methods, both from the viewpoint of homogenous incorporation of the granule over the soil profile to become treated as well as from possible premature loss of the gaseous active methyl isothiocyanate (MITC) by using improved tarping materials. Both result in lower environmental exposure and better biological performance of the application. In that respect, product incorporation in soil was studied in France and in Italy with more recent commercially available Basamid application machinery, and 29 plastic films have been compared for their MITC barrier properties with an 'in house' developed method. Film testing allowed clear categorizing in standard (monolayer) films, V.I.F. (Virtually Impermeable Film) and T.I.F. (Totally Impermeable Film). The paper presents the methodology for granule incorporation study and results from trials with two specific Basamid application machines compared with a classic rotovator, the methodology and comparison of plastic film barrier properties testing, and directives to minimize exposure and to maximize performance.     

Reductive soil disinfestation (RSD) alters gross N transformation rates and reduces NO and N2O emissions in degraded vegetable soils

Background and aims

Continuous vegetable cultivation in greenhouses can easily induce soil degradation, which considerably affects the development of sustainable vegetable production. Recently, the reductive soil disinfestation (RSD) is widely used as an alternative to chemical soil disinfestations to improve degraded greenhouse vegetable soils. Considering the importance of nitrogen (N) for plant growth and environment effect, the internal N transformation processes and rates should be well investigated in degraded vegetable soils treated by RSD, but few works have been undertaken.

Methods

Three RSD-treated and three untreated degraded vegetable soils were chosen and a ¹⁵?N tracing incubation experiment differentially labeled with ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ was conducted at 25 °C under 50 % water holding capacity (WHC) for 96 h. Soil gross N transformation rates were calculated using a ¹⁵?N tracing model combined with Markov Chain Monte Carlo Metropolis algorithm (Müller et al. 2007), while the emissions of N₂O and NO were also measured.

Results

RSD could significantly enhance the soil microbial NH₄ ⁺ immobilization rate, the heterotrophic and autotrophic nitrification rates, and the NO₃ ^? turnover time. The ratio of heterotrophic nitrification to total inorganic N supply rate (mineralization + heterotrophic nitrification) increased greatly from 5.4 % in untreated vegetable soil to 56.1 % in treated vegetable soil. In addition, low release potential of NO and N₂O was observed in RSD-treated vegetable soil, due to the decrease in the NO and N₂O product ratios from heterotrophic and autotrophic nitrifications. These significant differences in gross N transformation rates, the supply processes and capacity of inorganic N, and the NO and N₂O emissions between untreated and treated vegetable soils could be explained by the elimination of accumulated NO₃ ^?, increased pH, and decreased electrical conductivity (EC) caused by RSD. Noticeably, the NO₃ ^? consumption rates were still significantly lower than the NO₃ ^? production rates in RSD-treated vegetable soil.

Conclusions

Except for improving soil chemical properties, RSD could significantly alter the supply processes of inorganic N and reduce the release potential of N₂O and NO in RSD-treated degraded vegetable soil. In order to retard the re-occurrence of NO₃ ^? accumulation, acidification and salinization and to promote the long-term productivity of greenhouse vegetable fields, the rational use of N fertilizer should be paid great attention to farmers in vegetable cultivation.